pH-Dependent Behavior and Stability of Protein-Based Particles in Aqueous Media

Protein particles could enhance the stability of dispersions. This review focused on the characteristics of protein particles from different sources, their structural stability and the stability of dispersions at different pH values. Whey protein, sodium caseinate and gelatin particles were investigated. To create particles from these proteins, controlled aggregation and gelation were used in several methods. As chemical structures of these proteins are all different, their gelation properties also vary. Whey proteins are globular, caseins have a random structure, and gelatin in gelled form has triple helix structure. Whey proteins undergo thermal denaturation above 68ᵒC, therefore heat-set gelatin was often used for particle preparation. When whey protein particles were prepared at the iso-electric point (IEP) of proteins, they became dense and small; whereas at other pH values, particles were soft and spherical due to increased repulsive forces between proteins. Such particles could swell when the pH of the aqueous phase was away from the IEP. Sodium caseinate is more heat stable compared to whey proteins; however it is pH-sensitive. When sodium caseinate particles were prepared through acidification, particles were stable against disintegration only around the IEP of proteins. More stable caseinate particles could be produced using enzymatic crosslinking. On the other hand, gelatin particles, which were prepared via cold-set gelation, were stable over a wide pH range; however, as they were thermo-sensitive, particles disintegrated above 30ᵒC. This review explained the chemical differences of proteins, preparation of particles using different methods, and stability of particles and their dispersions at different conditions.